This invention relates to systems for the protection of secure areas, and to intruder detection systems. Specifically, it relates to an intruder detection system that can be integrated with a physical barrier and that is adapted to detect any physical deformation of the barrier or transgression of the area adjacent the barrier.
It is often necessary to protect equipment and secure areas from unauthorized, unwanted and sometimes hostile personnel and vehicles. Such protection conventionally includes fencing that encompasses the area or equipment to be protected. Intruder detection systems are also used in conjunction with fences or other physical deterrent barriers to enable responsible personnel to monitor the premises and to take appropriate action in response to detected intrusions.
In U.S. Pat. No. 4,327,358, issued Apr. 27, 1982 to the present inventor, there is disclosed an integrated physical deterrent barrier and intruder detection sensor that provides surveillance of intrusions in the airspace over the barrier. The sensor is coextensive with and mounted on the top of the barrier and is integrated into a barbed wire-topped chain link fence by arranging appropriately spaced parallel strands of barbed wire into a V configuration so as to form a corner reflector antenna at the system operating frequency. The active element of the corner reflecter is a leaky transmission line that extends the length of the corner reflector antenna, radiates RF energy and carries reflections from intrusion events back to a receiver and processing circuits. While the aforementioned device has proven to be effective, it has been found to be susceptible to false alarms caused by birds and other non-target intrusions far above the physical barrier.
In U.S. patent application Ser. No. 486,478 filed Apr. 19, 1983 by the present inventor, there is disclosed a secure area protection system in which a physical deterrent barrier, such as a coil of barbed wire, has a ported coaxial cable coextensive with and mounted within the barbed wire coil. The ported coaxial cable illuminates the tubular volume within the barbed wire coil with RF energy from the intrusion detection system transmitter. Variations in radio frequency reflections caused by physical deformations of the barbed wire coil are processed by detection system signal processing equipment to determine the incidence and location of intrusion events. The sensor may be integrated into a barbed wire coil positioned atop a chain link fence and supported by parallel strands of barbed wire inserted into notches formed in V-shaped supports atop the fence.
Since the radio frequency field is substantially confined within the tubular volume of the barbed wire coil, it is necessary that the coil be physically deformed in order to activate the intrusion sensor. While the aforementioned device have proven to be effective, it may be possible in certain instances for an intruder to gain access to the protected area by either bridging over the barbed coil or tunnelling under it. Furthermore, considerable time and effort may be expended to thread the ported coaxial cable within the barbed wire coil and, in one embodiment, to coaxially suspend the ported coaxial cable therein.